The general objective of this investigation is to determine the relationships of the vitamin D-induced intestinal brush border calcium- activated ATPase to calcium and phosphorus transport and to the isoenzymes of alkaline phosphatase (AP) in the intestine. Powerful inhibitors or intestinal brush border Ca-ATPase including ions, L- phenylalanine, methylated xanthines and diphosphonates will be used in vitro to inhibit in situ ATPase activity and calcium and phosphorus uptake under identical incubation conditions. A method measuring only ion flux into intestinal epithelial cells will be used to evaluate the transport role of Ca-ATPase. The effects of calcium and phosphorus on transport of the counter ion will be evaluated using this test system with ATPase results from a translation-dependent alteration of enzyme activity and substrate preference of AP without an increase in numbers of enzyme molecules will be tested. Resulting alterations of the proportions of the different isoenzymes of intestinal AP will be examined to determine if different chromatographic and electrophoretic forms of intestinal AP with different substrate preferences are induced by vitamin D as compared to the AP isoenzymes in control rachitic animals. Similar examination of the AP isoenzymes induced in intestine by glucocorticoids induce different forms of intestinal AP. Competition between the two steroidal hormones for a common AP messenger RNA molecule is proposed to occur, and is suggested to be the basis of antagonism between vitamin D and glucocorticoids on intestinal calcium transport.